1. Field of the Invention
The present invention relates to a nozzle touch apparatus in an injection molding machine, which is capable of automatically variably adjusting a nozzle touch force with advancement of an injection molding cycle.
2. Description of the Related Art
An injection molding machine is arranged to inject molten resin from an injection unit into a cavity defined by two mold halves respectively mounted on stationary and movable platens of a mold clamping unit, to thereby produce a molded product. To prevent leakage of the thus injected resin between a nozzle of the injection unit and a sprue bushing of the stationary mold half of the mold clamping unit, the nozzle is arranged to be in urged contact with the sprue bushing with a predetermined nozzle touch force. Further, maintenance of the injection unit is carried out, with the injection unit separated from the mold clamping unit. To this end, generally, the injection molding machine comprises a nozzle touch apparatus which operates to move the whole of the injection unit in the directions toward and away from the mold clamping unit.
A typical nozzle touch apparatus comprises an urging member which is driven by a hydraulic cylinder or an induction motor so as to be moved in the directions toward and away from the mold clamping unit. The urging member operates to urge the injection unit through a spring mounted on the urging member so as to move the injection unit toward the mold clamping unit. Arrival of the urging member to its moving position (wherein the spring is compressed by a predetermined amount to produce a predetermined nozzle touch force) is detected by a limit switch, a proximity switch or the like. That is, an adjustment of the nozzle touch force is effected by adjusting a position at which the detection switch is to be located. Accordingly, a difficulty is encountered in adjusting the nozzle touch force, in particular, during execution of an injection molding cycle. As a result, the resultant nozzle touch force may be excessive in magnitude. In this case, when a mold-opening state wherein no urging force is applied from a movable mold half to a stationary mold half in the direction opposite to that of the nozzle touch force is achieved, the stationary mold half 101, in particular, a hollowed and thin type of mold half such as a hot runner type of mold, and clampers 102 employed for mounting the stationary mold half onto the stationary platen are liable to be deformed, as shown in FIG. 3.